The present invention relates generally to systems and methods of controlling a fan to cool computer and electronic devices, components, and/or equipment enclosures, and more specifically to a system and method of controlling a cooling fan based on the sensed die temperature of a CPU. The presently disclosed system and method provide for reduced system power consumption and reduced audible fan noise.
In recent years, operating speeds of computer devices such as central processing units (CPUs) and microprocessors have undergone dramatic increases. Because increases in computer device speeds are typically accompanied by significant increases in the level of current flowing through the devices, the amount of heat dissipated by such computer devices has also risen dramatically. For this reason, there is a need for improved systems and methods of cooling computer devices and other electronic devices and/or components associated therewith to remove any excess heat that may cause high-speed computer systems to fail prematurely.
A conventional fan control system for cooling computer and electronic devices is disclosed in U.S. Pat. No. 6,188,189 (the '189 patent). As described in the '189 patent, a fan control system includes one or more temperature sensors such as thermal diode temperature sensors, and a pulse width modulation (PWM) control circuit operative to control the speed of a DC fan by varying the width of a PWM pulse. For example, a thermal diode temperature sensor may be implemented on an integrated circuit (IC) die of a CPU. In the event the sensed temperature of the CPU exceeds a predetermined maximum temperature Tmax, the PWM control circuit increases the PWM pulse width to increase the fan speed to its maximum level. In the event the sensed CPU temperature is less than a predetermined minimum temperature Tmin, fan cooling of the CPU device is deemed unnecessary, and the PWM control circuit therefore reduces the PWM pulse width to decrease the fan speed to zero. When the sensed CPU temperature falls within the range Tmin to Tmax, the PWM control circuit varies the PWM pulse width and consequently the fan speed linearly, i.e., the variation of the fan speed is linearly proportional to the sensed device temperature. The '189 patent further describes a power-up sequence for the fan control system, which includes spinning up the fan directly to its maximum speed for a limited time period upon power-up, before controlling the fan speed based on the sensed CPU temperature.
However, the conventional fan speed control system disclosed in the '189 patent has several drawbacks. For example, as described above, when the sensed CPU temperature is within the temperature range Tmin to Tmax, the system controls the fan speed so that it varies linearly over the range Tmin to Tmax. Although such linear control of the fan speed may maintain the CPU temperature within acceptable limits, it is generally ineffective at minimizing power consumption because the system including the fan control circuit and the computer device being cooled is typically dynamically nonlinear. Moreover, variations in power supply voltages, the ambient temperature, and the power dissipation of the CPU may contribute to the dynamic nonlinearity of the overall system. Accordingly, varying the fan speed linearly within the temperature range Tmin to Tmax may result in a fan speed and/or acceleration that is higher than necessary to cool the computer system, thereby causing increased system power consumption and increased audible fan noise. In addition, spinning up the fan directly to maximum speed during the fan power-up sequence may increase both the power consumption of the system and the audible noise of the fan.
Another conventional fan speed control system is disclosed in U.S. Pat. No. 6,601,168 (the '168 patent). As described in the '168 patent, a fan speed control system includes a temperature sensor operative to sense the temperature of an IC chip, and a fan controller operative to adjust the speed of a cooling fan to a target speed based on the sensed IC temperature. Specifically, the fan controller slowly adjusts the fan speed from an initial speed toward the target speed such that the audible noise associated with accelerating (or decelerating) the fan is reduced and therefore made less perceptible to the user of the computer system. However, although the fan speed control system of the '168 patent may reduce the audible fan noise, it may be incapable of minimizing the power consumption of the overall system.
It would therefore be desirable to have an improved fan control system and method for use in high-speed computer systems. Such an improved fan control system and method would be capable of maintaining the temperature of computer and electronic devices, components, and/or equipment enclosures at an optimal level for minimizing both the system power consumption and the audible fan noise.